Apparatus and method for recovering carbon black from pyrolysis byproducts

ABSTRACT

A system ( 10 ), process and apparatus are disclosed for purifying carbon black ( 15 ) containing sulfur and metal oxide impurities by digesting ( 20 ) the impure carbon black in an acid to extract the metal oxide ( 25 ). Sulfur ( 45 ) is then removed from the acid treated carbon black ( 30 ) by solvent extraction ( 35 ) with an organic aromatic solvent which is then recovered ( 50 ). The purified carbon black ( 40 ) is then suitable for use as a toner ( 60 ) by toner black processing ( 55 ).

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. ProvisionalApplication No. 60/256,005, filed Dec. 15, 2000, of the same or similartitle.

TECHNICAL FIELD

The present invention relates to the field of chemical processes, anddeals more particularly with a system, method, and apparatus forrecovering carbon black from pyrolysis byproducts. Still moreparticularly, the invention relates to a system, method, and apparatusfor removing impurities from carbon black produced as a byproduct of ascrap rubber pyrolysis system, resulting in a high purity carbon blackproduct suitable for use in such end products as inks, toners, tonercartridges, copiers, and other laser-type devices.

BACKGROUND ART

The literature is replete with various systems and methods forpyrolyzing scrap rubber, such as that found in worn out vehicle tires,into carbon black solids, low density hydrocarbon gases, and liquidhydrocarbon oil. Such a system is described in U.S. Pat. No. 5,894,012,issued to Denison, incorporated by reference, which describes apyrolysis subsystem, a carbon black refinement subsystem, and apyrolysis oil subsystem. Such systems accept feedstock consisting ofshredded vehicle tires, pyrolyze the shreds to produce hydrocarbons andan impure carbon black. The system may comprise additional subsystems tofurther refine the hydrocarbons and/or carbon black. These additionalsubsystems will remove any metals and fiberglass shards from the carbonblack byproduct for produce a fairly high grade carbon black containingmetal oxide particles and sulfur particles remaining from thedevulcanizaton action provided by the basic pyrolysis process.

It has been found through experience that while the carbon blackproduced by such systems can be of exceedingly high grade, it stillcontains chemical impurities which are difficult to remove. For example,carbon black reclaimed from scrap tires contains about 2.5 wt % sulfuras well as metallic impurities and silica, and these impurities areinherent in the carbon black resulting from the pyrolysis of tireshreds. Such impurities render this carbon black unsuitable for productswhich require a very highly refined grade of carbon black, such astoners for use in xerography equipment and laser printers. Such highlyrefined carbon black is normally produced directly from hydrocarbonswhich have few impurities to begin with, and not from scrap rubber whichcontains high amounts of sulfur and zinc compounds. If an economical waycould be found to further refine the carbon black resulting from variousscrap rubber pyrolysis processes of the prior art, then the value of thepyrolysis process could be enhanced by the higher marketability of theresulting carbon black byproduct. Such a product might also be highlycompetitive with existing processes producing toner black directly fromhydrocarbons.

Accordingly, what is needed is an improved system, process, andapparatus for refining and purifying carbon black produced as abyproduct of scrap rubber pyrolysis processes, and in particular, fromscrap rubber provided by shredded vehicle tires.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide animproved system, process, and apparatus for producing an extremely highgrade of carbon black by refining and purifying the carbon blacktypically produced as a byproduct of scrap tire pyrolysis processes.

Another object of the present invention is to provide an improved carbonblack purification system for producing marketable carbon black of apurity suitable for use in inks and toner cartridges.

It is another object of the present invention to provide an improvementto existing pyrolysis systems known to the art, by providing carbonblack purification subsystem for removing sulfur and metal oxideparticles typically contained in the carbon black byproduct of suchscrap tire pyrolysis systems.

It is another object of this invention to provide a carbon blackpurification system which will remove metal oxide and sulfur particlesfrom impure carbon black which may be available from any source.

It is a another object of this invention to provide a carbon blackpurification system which does not harm the environment by emittingpollutants or harmful waste byproducts.

It is another object of this invention to provide an continuous,automated, and precisely controlled system for purification of carbonblack to ensure uniform and consistent results.

It is another object of this invention to provide an carbon blackpurification system which continuously produces refined carbon black inindustrial quantities.

It is another object of this invention to provide a toner blackproduction capability for the production of toner black.

Other objects and advantages of the present invention will be set forthin part in the description and in the drawings which follow and, inpart, will be obvious from the description or may be learned by practiceof the invention.

To achieve the foregoing objects, and in accordance with the purpose ofthe invention as broadly described herein, the present inventionprovides a system, method, and apparatus for producing marketable carbonblack from carbon black byproducts typically provided by scrap tirepyrolysis systems. The process described herein has as its inputmaterial, or feedstock, a carbon black product containing contaminantssuch as metal oxide and sulfur particles. One embodiment of the processfor practicing the invention preferably comprises of a two steps. Onestep consists of using hydrochloric acid to remove any metal oxideparticles from the carbon black feedstock. The other step consists ofusing a solvent to remove the sulfur particles from the remaining carbonblack feedstock. The two steps can be performed in any order.

In another alternative embodiment, the process may further comprise atoner black step, wherein the carbon black from which the metal oxideand sulfur particles have been removed is combined with magnetite (blackiron oxide) and small amounts of flow control agents and toner modifyingagents to create a high quality toner black suitable for use in such endproducts as inks and toner cartridges.

The invention teaches the use of a closed solvent recovery process, inwhich solvent used in the solvent extraction step is recovered andreused from a closed system. This closed solvent recovery processeliminates the requirement for continuous supplies of solvent to theprocess by capturing the solvent vapor, condensing it, and returning itto the solvent extraction process. This prevents release of solventvapors into the surrounding atmosphere, reduces the risk of hazardouslevels of toxic materials, and provides a safe workplace for workersinvolved in the processing of carbon black. The invention furtherteaches the use of a closed steam generation process, in which the watervapor used in the form of steam for drying and evaporation throughoutboth steps of the invention and the water used for dilution within themetal oxide extraction step are captured and retained for reuse withinthe system. The water used within the system must be free of minerals inorder to reduce scale and mineral deposits within water transmissionpaths of the system. This may be accomplished by continuous use ofdistilled water. However, by reusing a fixed amount of distilled waterwithin a closed system in the manner taught by the invention, therequirement for continuous distilled water by the system is kept to aminimum.

The technique comprising the invention requires sufficient amounts ofsolvent, hydrochloric acid, and an acid neutralizing agent to remove theimpurities. Hydrochloric acid and the neutralizing agent are used insuch a way as to produce harmless salts as a waste byproduct, and thesolvent is employed in a closed system which results in no release ofsolvent vapors to the atmosphere. The result is a process which isbenign to the environment and acceptable under current federalregulations of the Unites States Government which control toxicemissions from commercial and industrial processes.

The present invention will now be described with reference to thefollowing drawings, in which like reference numbers denote the sameelement throughout.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the invention, will be better understoodwhen read in conjunction with the appended drawings. For the purpose ofillustrating the invention, there are shown in the drawings embodimentswhich are presently preferred. It should be understood; however, thatthe invention is not limited to the precise arrangements andconfigurations shown. In the drawings, like numerals are used toindicate like elements throughout. In the drawings:

FIG. 1 is a block diagram showing the major functions comprising anembodiment of the invention;

FIG. 2 is a block diagram showing the major functions comprising anotherembodiment of the invention;

FIG. 3 is a detailed schematic diagram showing an embodiment of anapparatus designed to practice the metal oxide extraction and solventextraction steps of the invention; and,

FIG. 4 is a block diagram illustrating the primary steps comprising thetoner black step.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention defines techniques for the refinement andpurification of carbon black feedstock containing impurities so as torender it suitable for use in toner black applications. The invention isillustrated schematically in FIG. 1, wherein an embodiment 10 of aprocess practicing the invention is shown. Feedstock 15 for the processgenerally consists of unrefined carbon black material containingimpurities which render it unusable for toner black as required by inks,laser printers, copiers, and the like. If the impure carbon blackfeedstock 15 is the result of a scrap rubber pyrolysis process, it willgenerally contain metal oxides (primarily zinc oxide, ZnO, about 5% byweight) and sulfur (about 2.5% by weight), but no solid impurities suchas metal fragments or fiberglass. The sulfur is in the form of physicalparticles and is not in chemical combination with the carbon black,since the scrap rubber is typically devulcanized during the pyrolysisprocess. Carbon black produced as a byproduct of a pyrolysis process forscrap rubber tires, as described in U.S. Pat. No. 5,894,012, ispreferably used as feedstock to the present process, although otherfeedstocks having similar composition may also be used without departingfrom the scope of the invention. The process also requires Quantities ofhydrochloric acid and a neutralizing agent for the digestion of metaloxides from the carbon black feedstock. The preferable neutralizingagent is sodium hydroxide, or caustic soda, chosen primarily for itsavailability and cost. Other alkaline compounds may also be used as aneutralizing agent without departing from the concept and scope of theinvention. A quantity of solvent is used for the chemical removal of thesulfur impurities and continuously recycled. The solvent is preferablybenzene, xylene, or toluene, with toluene being the most preferablesolvent. The resulting outputs of the process are refined carbon blacksuitable for use in toner cartridges, pure sulfur, and waste solidscomprised primarily of various salts, ZnCl₂, and other metal chlorides.

In a preferred embodiment, as shown in FIG. 1, the process 10 mayconsist of three stages. The first stage consists of Metal OxideExtraction Process 20 in which all metal oxides are removed from theunrefined feedstock material 15, also referred to as “digesting” thematerial, using dilute hydrochloric acid (HCl). The concentration orstrength of the dilute HCl solution is chosen to ensure that the volumeof liquid in the slurry thus formed in the Metal Oxide ExtractionProcess 20 is sufficient to allow it to be easily handled. The metaloxide products 25 are non-toxic and may be discarded by standard methodssuch as land fill. The second stage, or Solvent Extraction Process 35,receives the carbon black feed stock 30 with all metal oxides removedand removes sulfur from the material processed through the first stage.The solvent will dissolve the sulfur out of the carbon black feedstock30 produced from the first stage to provide a highly refined carbonblack material 40 and sulfur solid wastes 45. An optional third stageconsists of a Toner Black Process 55 which accepts the now purifiedcarbon black 40 and adds components to produce a toner black product 60.

The solvent used in the Solvent Extraction Process 35 may be benzene,toluene, or xylene, but the preferred solvent is reaction grade toluene.The solvent is added to the sulfur bearing material 30 and, usingagitation at the proper temperature, the sulfur is dissolved, dried, andremoved from the system as sulfur solids wastes 45. Note that carbondisulfide can also be used as solvent, but its use is discouraged due tothe instability of the solvent at the temperatures used herein and thedanger in handling. A Solvent Recovery Process 50 is provided to recyclethe solvent and prevent gross escape of hazardous vapors. This closedloop system recovers the solvent through evaporation once it has beenused to remove the sulfur particles. A Closed Loop Steam Generation andRecovery Process 65 is provided to supply heated heat exchange fluid,normally water, to various components of the Solvent Extraction Process35 and condensed water to the Metal Oxide Extraction Process 20 fordiluting the hydrochloric acid. Condensate is collected at variouspoints from the Solvent Extraction Process 35 and recycled through thesteam generation process.

In an alternative embodiment 70 of the invention, as shown in FIG. 2,the sequence in which the steps of metal oxide extraction and solventextraction are performed is reversed. The Solvent Extraction Process 36first receives the impure carbon feedstock 16 and removes sulfur andsulfur compounds therefrom. The solvent will dissolve the sulfur out ofthe carbon black feedstock 16 to provide a sulfur byproduct 46 and acarbon black feedstock material 41 without sulfur content but containingmetal oxides. This carbon black material 41 is passed to a Metal OxideExtraction Process 21 in which all metal oxides are removed using dilutehydrochloric acid. The Metal Oxide Extraction Process 21 produces metaloxide solids 26 as a byproduct and a highly refined and purified carbonblack material 31. The metal oxide solids 26 are non-toxic and may bediscarded by standard methods such as land fill. An optional third stageconsists of a Toner Black Process 56 which accepts the now purifiedcarbon black 31 and adds components to produce a toner black product 61.A Solvent Recovery Process 51 is provided to recycle the solvent andprevent escape of hazardous vapors from the system. This closed loopsystem recovers the solvent through evaporation once it has been used toremove the sulfur and sulfur compounds. Additional amounts of solventare supplied as needed from a supply tank to replenish small amountswhich may be lost in processing. A Closed Loop Steam Generation andRecovery Process 66 is provided to supply heated heat exchange fluid,normally water, to various components of the Solvent Extraction Process36 and condensed water to the Metal Oxide Extraction Process 21 fordiluting the hydrochloric acid. Condensate is collected at variouspoints throughout the Solvent Extraction Process 36 and recycled throughthe steam generation process. It should be noted that embodiment 10presents a slight advantage over embodiment 70, particularly when thesolvent selected for solvent extraction processing is toluene. Withinthe Solvent Recovery Process 65, 66, the solvent is heated to atemperature in excess of the boiling point of water, as will bepresently seen, in order to vaporize the toluene and remove it from thesolid product. This toluene vaporization coincidentally removes anywater which may be retained in the carbon black feedstock, since theboiling point of water is less than that of toluene. This providesembodiment 10 with an additional opportunity for water removal from thefinal carbon black product which is not present when the SolventExtraction Process is performed prior to the Metal Oxide ExtractionProcess, as in embodiment 70.

In another embodiment of the invention, the Toner Black Process may beomitted so that highly purified carbon black is produced as a result ofperforming the Metal Oxide Extraction and Solvent Extraction Processeson the impure carbon black.

In another embodiment of the invention, the Closed Loop Steam Generationand Recovery system may be omitted when inexpensive sources of highlypurified water are available or when mineral buildup within the conduitsconducting condensate and/or steam is not a concern.

In another embodiment of the invention, the Solvent Recovery Process maybe omitted when the carbon black purification and refinement process inused in conjunction with other industrial processes.

Attention is now directed to FIG. 3, which shows a detailed schematicflow illustrating the process and method of an embodiment of theinvention. During the first stage of the purification and refinementprocess, carbon black feedstock material 100 is digested withhydrochloric acid (HCl) in a specially constructed tank to form metallicchlorides in solution. The resulting solution is then neutralized withan alkaline neutralizing agent and the waste metal oxides are removedfrom the remaining solid carbon black material. Carbon black feedstock100 consists of granular carbon black containing impurities comprisingprimarily sulfur and metal oxide particles. The feedstock 100 maycontained in a hopper (not shown) for temporary storage prior toprocessing or it may be provided directly from a prior processing systemwithout intermediate storage. In either case, it is continuously sent tothe mixing tank 110 by a standard conveyance means known to theindustry, such as by a conveyor, auger, or similar apparatus; a screwtype conveyor is preferably used to control the rate at which the carbonblack feedstock 100 is delivered and to maintain a closed system. Dilutehydrochloric acid is also sent to mixing tank 110 through conduit 105where it combines with feedstock 100 in a mixing zone 112 therein toform a acidic slurry comprised of carbon black particles and (possibly)sulfur particles admixed in an acidic solution wherein the hydrochloricacid chemically reacts with the metal oxide particles to form metalchlorides in solution.

Concentrated hydrochloric acid (HCl) is contained in acid storage tank130 where it is kept upon delivery to the facility until ready for use.As hydrochloric acid is expended in the process, new supplies arebrought to acid storage tank 130 from external sources which are notdepicted in FIG. 3. Pump 132 delivers the concentrated hydrochloric acidfrom acid storage tank 130 through conduit 134 to the acid dilution tank102, where it is combined with water through conduit 136. The source ofthe water supplied by conduit 136 will be discussed later. The strengthof the diluted hydrochloric acid must be sufficient to digest the metaloxides out of the carbon black but must also result in a slurry that hassufficient volume and density of liquid to allow it to be easily handledin a continuous manner by the equipment. A concentration of 3 normal(3N) has been found in practice to contain too little liquid forconvenient handling, and a concentration of 1N gives too much volume ofliquid, although both values are sufficient to digest the metal oxides.The dilute hydrochloric acid solution contained in acid dilution tank102 is preferably maintained at a concentration of approximately 2N,although any suitable concentration may be used and still be within thescope of the invention.

Mixing tank 110 is comprised of a specially built tank vat, orcontainer, which encloses and defines mixing zone 112. A mixing means isassociated with mixing tank 110 and comprises a high shear agitator 114within mixing zone 112, and a pump-around circuit consisting of pump116, conduit 118, valve 120, and return conduit 122. The pump-aroundcircuit is used to remove slurry from the bottom region of the mixingzone 112 and reintroduce it into the top region of mixing zone 112 inorder to maintain and control the hold-up time that the slurry stays inthe mixing zone 112. The pump-around circuit is also used to maintainconsistency of the acidic slurry therein by keeping the carbon blackparticles admixed within the liquid in conjunction with the action ofthe high shear agitator 114. The acid slurry remains in mixing tank 110where it is continuously mixed by the flow-through circuit and mixed andagitated by high shear agitator 114. Valve 120 initially directs theflow of acid slurry from conduit 118 to return conduit 122 until thelevel of the slurry within acid mixing tank 110 has initially reached adesired level, at which point valve 120 partially opens to split theacidic slurry stream between return conduit 122, which channels aportion of the acidic slurry back to mixing tank 110, and conduit 123,which channels a portion of the slurry into neutralization tank 140.

It should be appreciated that although single tanks, conduits, and pumpsare shown in the schematic diagram, multiple components may be usedwithout departing from the scope of the invention. A series of suchmixing tanks 110 may be used to maintain a continuous process or asingle tank can be employed in a batch mode, each configuration beingcontemplated within the scope of the present invention. Alternatively, aseries of two or more mixing tanks 110 could be employed with staggeredtimes of filling and emptying. Also, a single tank could be envisionedto operate in a continuous mode wherein it is being constantly filledand emptied at compatible rates. Nothing in this description should beconstrued as confining the number of such mixing tanks to a particularnumber or of limiting the defined digestion process to either acontinuous or batch mode of operation.

The acidic slurry pumped by pump116 through conduits 118, 123 into aneutralization tank 140 is neutralized by the introduction therein of anappropriate amount of an alkaline neutralizing agent from storage tank150. The neutralizing agent is preferably sodium hydroxide (NaOH, orcaustic soda) but other alkalines may also be used without departingfrom the intent and scope of the invention. Standard delivery means areused to deliver the neutralizing agent to storage tank 150 where it isstored for subsequent use in the process. The amount of neutralizingagent used to neutralize the slurry is controlled by metering pump 152which pumps the neutralizing agent from storage tank 150 through conduit154 into neutralization tank 140. Metering pump 152 is responsive to apH meter 156 which measuring the pH of the neutralized slurry as itexits neutralization tank 140, so that the precise amount ofneutralizing agent can be introduced to maintain a neutral pH of 7therein. The neutralization process causes a chemical reaction betweenthe alkaline neutralizing agent and the remaining acid to form waterwith metal chloride salts and possibly other salts in solution.

A separation means is provided for separating the metal chlorides andother salts from the neutralized slurry. The neutralized slurry isdelivered by pump 160 through conduit 165 into a separation means 170which separates the aqueous solution containing the dissolved salts fromthe feedstock solids from which the metal oxides have been removed andwhich now may contain only carbon black and sulfur particles. Separationmeans 170 is preferably a centrifuge type device, and most preferably apusher-type centrifuge which removes the feedstock particles of carbonblack and sulfur while maintaining a small particle size. Other types ofseparation means such as filtration devices employing gravity or vacuumtechniques may also be used without departing from the scope of theinvention. The aqueous solution containing dissolved salts coming fromthe separation means 170 is pumped by pump 175 into evaporator 180 wherethe water is removed to leave only waste solids 185 consisting of saltsof zinc and other metals, which are then removed from the system wherethey are either recycled by other industrial processes or disposed of insome environmentally safe manner. The feedstock particles provided fromseparation means 170 are transported by a conveyance means to dryer 190to remove any remaining excess water. The conveyance means is preferablya rotary screw conveyor to provide a continuous and uniform flow ofcarbon black to dryer 190 and to maintain a closed system for therecovery of water by the Steam Generation and Recovery System for reuse,which shall be described later. Other conveyance means such as an auger,bucket conveyor, pneumatic conveyors, gravity, or similar devices may beused when a closed system is not desirable, without departing from thescope of the invention. The water vapor resulting from the dryingprocess and removed from the carbon black is collected as it condensesand is directed to condensate collection tank 300.

During the second stage of the purification and refinement process,sulfur particles are removed by solvent extraction, the solvent isrecovered for re-use, and the resulting solids are dried to produce purecarbon black. The solvent is chosen for its ability to dissolve sulfurfrom the carbon black feedstock. The solvent selected for the processmay preferably be benzene, xylene, or toluene, and most preferablytoluene. The carbon black feedstock containing sulfur particles, comingfrom dryer 190 is introduced into solvent mixing tank 200. This tank,like mixing tank 110, contains a mixing means consisting of a high shearagitator 201 for mixing the solids with the chosen solvent and a heatingmeans for holding the solution at an elevated temperature preferably inthe range of between approximately 60° C. and approximately 80° C. Thecarbon black feedstock from dryer 190 is added to a quantity of solventin mixing tank 200. The solvent is preferably provided from solventcollected downline from the mixing action by condenser 260 but may alsobe optionally provided from solvent storage tank 270. The solvent willdissolve the sulfur particles and the agitation action of the high shearagitator 201 will maintain a solvent slurry in the solvent mixing tank200 consisting of carbon black particles admixed in a solution ofsolvent containing dissolved sulfur. This solvent slurry is pumped viapump 210 into a separation means 220 where the carbon black solidportion is separated from the solvent/sulfur liquid portion. Separationmeans 220 is preferably a centrifuge, and most preferably a pusher-typecentrifuge which removes the carbon black while maintaining a smallparticle size. Other types of separation means such as filtrationdevices may also be used without departing from the scope of theinvention. These carbon black solids are removed via a conveyance means225 to dryer 230 where they are dried to remove any remaining solvent.The conveyance means 225 is preferably a screw type conveyor so that thesolvent is kept within a closed system and so that the carbon blacksolids may be moved at a continuous uniform rate, but other means ofmoving the carbon black which are functionally equivalent may be usedwithout departing from the scope of the invention. The dried carbonblack solids 240 emerging from dryer 230 are then either stored fortransportation to other locations, pelletized and bagged for shipping,or processed into toner black by a succeeding stage of the system. Thesolvent/sulfur liquid removed from centrifuge 220 is pumped by pump 235into evaporation means 250 where the solvent is separated from thesulfur residue by means of evaporation. The evaporation means 250 ispreferably a single or multiple effect evaporator of a type well knownin the industry, but other types of evaporators may be used withoutdeparting from the scope of the invention. Evaporation is accomplishedwithin evaporation means 250 by a heat transfer fluid which ispreferably water in the form of steam. In the case where the solvent istoluene, the use of steam requires it to be superheated since theboiling point of toluene 110° C. and the boiling point of water is 100°C. The sulfur 255 removed from evaporation means 250 is of high qualityand purity and can be either sent to other locations for use in otherprocesses or discarded in an environmentally safe manner such as alandfill.

The apparatus used to practice the invention employs a Solvent RecoverySystem for containing solvent vapors for reuse and preventing the vaporsfrom creating an environmental hazard by escaping into the atmosphere.Condenser 260 is provided for condensing the solvent vapor which isproduced from either evaporation means 250 or dryer 230. When a SolventRecovery System such as the one described herein is employed inconjunction with the carbon black purification and refinement system, itis assumed that evaporation means 250 and dryer 230 are enclosed so asto prevent loss of any vapors or gases produced therein. Althoughcondenser 260 can be of any suitable design, the preferred configurationis that of a standard shell and tube heat exchanger. Condenser 260preferably uses chilled water to condense the solvent vapor, but othersuitable heat transfer fluids used in cooling applications and wellknown to the art may be used without departing from the scope of theinvention. The liquid solvent resulting from such condensation iscollected in the lower portion of condenser 260 in a collection areawhich is not shown in the diagram but which is part of condenser 260.When it is required for replenishing the liquid in solvent mixing tank200, it is pumped from condenser 260 into solvent mixing tank 200 bypump 265. If insufficient amounts of solvent are available fromcondenser 260, an additional amount of solvent may be obtained for usein solvent mixing tank 200 by pumping it from the solvent storage tank270 by pump 275. Normally, the amounts of solvent supplied by solventstorage tank 270 are expected to be for priming the system initiallywith sufficient solvent for the overall process.

A closed loop Steam Generation and Recovery System is provided to supplysteam to various components of the system for heating, drying, and/orevaporation, to collect the condensate resulting from the steamcondensation, to collect the condensate evaporated from the processmaterials, and to recycle both back through the system. A closed loopsystem such as the one described herein is used to prevent build-up ofscale and other minerals in the pipes comprising the system and to keepimpurities from possibly contaminating the materials being processed.Steam generator 280 produces either steam or superheated steam,depending upon the heating requirements of the particular systemcomponent. Normal steam is employed by dryer 190, evaporator 180, andsolvent mixing tank 200. Superheated steam is used by evaporation means250. When each component has used the caloric content of the steamprovided to it by steam generator 280 through condensation of the steam,the resulting condensed water is collected in condensate collection tank290 for reuse within the system. It is normally pumped by pump 295 intoacid dilution tank 102 to dilute the hydrochloric acid for use in thefirst stage of purification and refinement, since, being distilled, itis expected to have no impurities which might contaminate the process. Asecond condensate collection tank 300 is used to hold both thecondensate resulting from evaporation in evaporator 180, the condensatefrom the steam used to evaporate the condensate within evaporator 180,and the water removed from the carbon black in dryer 190. A source ofdistilled water (not shown) is used to supply the closed loop systemwith its initial supply of working fluid. This source is also used toreplenish fluid lost through pressure relief or leakage, but this amountof loss is negligible. It should be noted that the number of condensatecollection tanks and the choice of tank for collecting the condensate ofa particular piece of equipment is arbitrary and dependent upon theplant layout of the system as it is physically configured.

A third stage of the carbon black refinement and purification processmay be alternatively used to process refined carbon black into a tonerblack product. The toner black process 300 depicted in FIG. 4illustrates such a stage. The pure carbon black 305, from which metaloxides and sulfur have been removed, may be immediately processed at thesite by standard methods known to the industry. This method involvescollecting the pure carbon black 305 in a suitable solids bin 320 forprocessing and then mixing with a suitable grade of magnetite 310 frombin 325 and a styrene-acrylic resin 315 from bin 330 to preventclumping. Other materials, such as titanium dioxide coated with organiccompounds to improve flowability, may also be advantageously added tothe mixture through bin 330 as needed for various customers' needs. Thisdry mixture of carbon black, magnetite, and resin is combined in bin 335and then provided to an extruder 340 of common design known to the art,preferably a twin screw extruder, where it is heated to a temperaturenecessary to melt the resin so that it coats the particles of carbonblack and magnetite. The heated mixture is then extruded through anextruder die to form a column. The extruded column is then formed intopellets by a standard means known to the industry, such as a rotatingknife or cutter. The pellets are allowed to fall into a hammer mill 345,preferably by action of gravity. The hammer mill 345 pulverizes thepellets and form a fine toner black powder 350. This powder 350 may bystored in bin 355 for later packaging and shipment; optionally thepellets may also be packaged and shipped.

The practice of the invention does not depend upon the order in whichthe digestion step and the solvent extraction step are performed. Theprocess shown in FIG. 3 is illustrative of embodiment 10 in FIG. 2. Inan alternative embodiment 70 (FIG. 3) of the invention, feedstock 100could be first fed to solvent mixing tank 200 for solvent extraction ofsulfur. The resulting carbon black intermediate product, after recoveryof the solvent containing sulfur, could then be fed to tank 110 fordigesting with acid and subsequently to tank 140 for neutralization ofthe resulting acid solution. The apparatus used for separation, drying,evaporation, and dilution could be easily be reconfigured by one skilledin the art according to the requirements of the order of the steps asshown in FIG. 3.

As has been demonstrated, the present invention provides an advantageoussystem, method, and apparatus for the production of a pure carbon blackfrom feedstock containing significant amounts of metal oxide and sulfurparticulate matter, such as the carbon black produced from the pyrolysisof scrap automobile tires. The system operates continuously and not inbatches to provide a constant rate of product being produced.Furthermore, the system is closed in the sense that both the solvent andthe cooling fluid used in various parts of the equipment are recoveredand reused. In the case of a toxic solvent, this reuse provides thefurther benefit of safety for workers and conformance with governmentalregulations controlling the release of hazardous substances. Theresulting high quality carbon black can be further processed to formtoner black for use in toner cartridges for laser printers andxerography equipment. The cost of purified and refined carbon blackproduced according to the invention compares favourably with thatproduced directly from hydrocarbons by more conventional methods.

The present invention has been described with reference to blockdiagrams illustrating systems, methods, and devices according toembodiments of the invention. It will be understood that each block ofthe block diagrams, and combinations of blocks in the block diagrams,can be implemented by similar components providing the same orsubstantially the same functions. While the preferred embodiments of thepresent invention have been described, additional variations andmodifications in those embodiments may occur to those skilled in the artonce they learn of the basic inventive concepts. Therefore, it isintended that the appended claims shall be construed to include both thepreferred embodiment and all such variations and modifications as fallwithin the spirit and scope of the invention.

1. A method for purification and refinement of carbon black comprisingthe steps of: providing a feedstock comprising a physical combination ofparticulate carbon black, metal oxides, and sulfur; removing the metaloxide particles from the feedstock by introducing the feedstock into anaqueous acidic solution, wherein the aqueous acidic solution dissolvesthe metal oxide particles from the feedstock; and, removing the sulfurparticles from the feedstock by introducing the feedstock into asulfur-dissolving solvent to produce a sulfur-containing slurry, whereinthe sulfur-dissolving solvent dissolves the sulfur from the feedstock;separating the feedstock from the sulfur-containing slurry; evaporatingall sulfur-dissolving solvent from the sulfur-containing slurry;removing the sulfur remaining after evaporation of the sulfur-dissolvingsolvent; and reusing the sulfur-dissolving solvent.
 2. The method ofclaim 1 wherein the step of removing metal oxide particles comprises thesteps of: mixing the feedstock with an aqueous acidic solution tochemically react with the metal oxides and form an acidic slurrycomprising metal salts in solution; and separating the acidic slurry andthe feedstock.
 3. The method of claim 2, wherein the aqueous acidicsolution is hydrochloric acid.
 4. The method of claim 3, wherein theaqueous acidic solution has a concentration of 2N.
 5. The method ofclaim 1, wherein the step of removing sulfur particles further comprisesheating the sulfur-containing slurry to a selected temperature of lessthan 110° C.
 6. The method of claim 1, further comprising the steps of:agitating the sulfur-containing slurry at a temperature selected tomaintain the sulfur and admixed carbon black particles in solution;removing the feedstock from the sulfur-containing slurry; separating thedissolved sulfur from the sulfur-containing slurry by evaporating thesulfur-containing solvent; and recycling the resultant sulfur-dissolvingsolvent.
 7. The method of claim 6, wherein the step of separating thedissolved sulfur from the sulfur-containing slurry is accomplishing byevaporating the sulfur-dissolving slurry to produce sulfur-dissolvingsolvent vapor and sulfur solids.
 8. The method of claim 1 wherein thestep of removing the sulfur particles from the feedstock by introducingthe feedstock into a sulfur-dissolving solvent to produce asulfur-containing slurry comprises the step of: agitating thesulfur-containing slurry at a temperature in a range of betweenapproximately 60° C. and approximately 80° C., wherein the carbon blackparticles are admixed in the sulfur-dissolving solvent containingdissolved sulfur.
 9. The method of claim 1, further comprising the stepof: mixing toner black components to the feedstock to form a tonerportion.
 10. The method of claim 9, wherein the toner black componentsare comprised of magnetite and a resin.
 11. The method of claim 10,further comprising the step of: extruding the toner portion to formpellets.
 12. The method of claim 11, further comprising the step of:pulverizing the pellets to form a powder.
 13. A process for purificationand refinement of a carbon black feedstock comprised of a physicalmixture of carbon black, metal oxide, and sulfur particles, the processcomprising the steps of: providing the feedstock at a continuous anduniform rate; mixing the feedstock with an aqueous solution containingan acid to chemically react with the metal oxide particles contained inthe feedstock and form a first liquid portion and a first solid portion,the first liquid portion comprising an acid slurry comprising metalsalts in solution, the first solid portion comprising feedstockparticles; separating the first liquid portion from the first solidportion; adding the first solid portion to a sulfur-dissolving solventto form a solvent slurry, wherein the sulfur particles contained in thefirst solid portion are dissolved by the sulfur-dissolving solvent;agitating the solvent slurry at a temperature in a range of betweenapproximately 60° C. and approximately 800° C., in order to maintain thesolvent slurry having a second liquid portion comprising a solution ofsulfur-dissolving solvent and the sulfur and a second solid portioncomprising admixed feedstock particles; removing the second solidportion; evaporating the sulfur-dissolving solvent from the remainingsolvent slurry to provide solid sulfur; and condensing thesulfur-dissolving solvent for reuse.
 14. The method of claim 13, furthercorriprising the step of: neutralizing the first liquid portion with analkaline solution.
 15. The method of claim 14, wherein the alkalinesolution is comprised of sodium hydroxide.
 16. The method of claim 13,wherein the sulfur is separated from the sulfur-dissolving solvent by anevaporation means within a closed system.
 17. A method for purificationand refinement of carbon black comprising the steps of: providing afeedstock comprising a physical combination of particulate carbon black,metal oxides, and sulfur; removing the metal oxide particles from thefeedstock by introducing the feedstock into an aqueous acidic solution,wherein the aqueous acidic solution dissolves the metal oxide particlesfrom the feedstock; removing the sulfur particles from the feedstock byintroducing the feedstock into a sulfur-dissolving solvent to produce asulfur-containing slurry, wherein the sulfur-dissolving solventdissolves the sulfur from the feedstock; and, neutralizing the aqueousacidic solution with an alkaline solution.
 18. The method of claim 17,wherein the sulfur-dissolving solvent is selected from a group composedof xylene, benzene, and toluene.
 19. The method of claim 17, wherein thealkaline solution is comprised of sodium hydroxide.
 20. The method ofclaim 17, further comprising the step of filtering the feedstock fromthe sulfur-containing slurry; and evaporating the sulfur-dissolvingsolvent from the sulfur-containing slurry from which the feedstock hasbeen removed, wherein the sulfur is removed and the sulfur-dissolvingsolvent is reused.
 21. The method of claim 20, wherein the step ofevaporating the sulfur-dissolving solvent from the sulfur-containingslurry further comprises heating the sulfur-containing slurry to aselected temperature of less than 110° C.